Effect of subsoiling on soil physical properties and dry matter productionon a Brown Soil in Southland, New Zealand

This study examined the effect of shallow subsoiling on soil physical prope rties and ryegrass-white clover pasture production on a Waikiwi silt loam ( Brown Soil) over 2.5 years. Macroporosity, hydraulic conductivity, and air permeability were measured in 6-cm increments down to 30 cm soil depth. The topsoil was loosened by pulling both conventional tines or wing-shaped tin es set at 50 cm apart through the soil, at a depth of 25-30 cm. Subsoiling increased macroporosity by up to 39% of the soil volume, and increased satu rated hydraulic conductivity and air permeability by up to two orders of ma gnitude. Improvements in soil physical conditions were evident for up to 2 years after subsoiling with both the winged tines and conventional tines, a lthough there were few differences between the tine types. Some recompactio n and settling over time occurred in the upper 12 cm of the soil profile. F or the second year, the conventional tine subsoiling treatment reduced tota l production by 9%. Pasture dry matter production for the winged tine subso iling treatment was variable with no significant differences in total produ ction compared with non-subsoiled controls.